1. Field of the Invention
The present invention relates to brake mechanisms for electric motors and the like. More particularly, the invention relates to brake mechanisms wherein a friction disk secured to the rotatable shaft of an electric motor is engaged to effect a braking action that prevents or stops rotation of the shaft.
2. Reference to Prior Art
Brake mechanisms such as illustrated in U.S. Pat. Nos. 4,181,201 and 4,798,269, incorporated herein by reference, are typically utilized to prevent or stop rotation of the shafts of electric motors. The brake mechanism is located outside one end of the housing of the electric motor and includes a brake disk assembly secured to the motor shaft for rotation therewith. The rotating brake disk assembly is clamped or frictionally engaged between two braking surfaces to effect a braking action that prevents or stops rotation of the shaft. The first braking surface is typically a fixed brake pad mounted on the outer side of the end wall of the electric motor. The second braking surface is a brake shoe that is moved into frictional engagement with the brake disk assembly under pressure exerted by a pivoting lever. The lever moves the brake shoe toward and against the brake disk assembly under pressure exerted by a compression spring. To permit rotation of the motor shaft, the lever is pivoted away from the brake shoe by energizing a solenoid or similar electromagnetic device, thereby interrupting the spring pressure moving the brake shoe away from the brake disk. To stop rotation of the shaft, power to the solenoid is interrupted so that the spring pressure pivots the control lever against the brake shoe, thereby moving the brake shoe against the brake disk assembly. Brake mechanisms operating in this manner are typically known as spring set, magnetically released brakes.
The brake disk assembly for such brake mechanisms typically includes a hub secured to the motor shaft for rotation with the motor shaft, and a friction disk mounted on and surrounding the hub. When the friction disk is sandwiched or engaged between the brake shoe and the brake pad, frictional forces stop rotation of the shaft.
In one prior art arrangement, the hub is a relatively thick, ring-shaped member produced by machining a metal block or rod. The hub includes opposed end surfaces, a central bore extending between the end surfaces for receiving the motor shaft, a longitudinal axis coextensive with the longitudinal axis of the bore, and an outer periphery spaced from the central bore. A plurality of splines are spaced around the outer periphery. The splines extend between the end surfaces and parallel to the longitudinal axis of the hub. Each spline includes a radially outer surface, and a pair of spaced sides extending radially inwardly from the outer surface toward a root portion or groove which spaces each spline from adjacent splines. The splines have equivalent widths measured across the outer surface in the circumferential direction of the hub. Two set screw bores offset ninety degrees from each other extend radially inwardly from the root portion of the splines to the central bore for receiving set screws to secure the hub to the motor shaft. Also in this arrangement, the friction disk is a relatively thin, disk-shaped member surrounding the outer periphery of the hub. The friction disk includes opposed friction surfaces, a central aperture extending between the friction surfaces for receiving the hub, and an outer periphery spaced from the central aperture. The shape of the central aperture is complementary to the outer periphery of the hub. The aperture includes spline recesses for receiving the hub splines, and the friction disk also includes splines which are received in the grooves between the hub splines.